Contemporary computer and communications systems commonly comprise several subsystems, each implementing one or more computation or communication functions. Examples include compute servers, Internet web servers, storage servers, and packet-based communications switches. Each subsystem includes its unique electrical and mechanical elements, including printed-circuit wiring board assemblies, internal wiring and connectors, etc. Each subsystem is outfitted with external connector sockets for communicating with other subsystems and for drawing power. The subsystems are mounted in proximity to each other in mechanical structures in the form of industry standard sized racks or custom-sized chassis.
FIG. 1 illustrates a representative contemporary computing center having two servers 10 and a data storage 11. The servers 10 include subsystems 12 that are housed in industry-standard 19-inch racks. The subsystems 13 of the storage 11 are housed in a custom-size chassis. The servers 10 and storage 11 are typically in an environmentally controlled data center or server room. The subsystems 12–13 are interconnected with each other and to outside communication links through electronic or optical cables 16. AC or DC electrical power must also be supplied to the subsystems 12–13 and is typically distributed via under floor cabling 15 from a power source.
The rack/chassis-based architecture of FIG. 1 has several advantages: (1) the subsystems may be arbitrarily arranged in the room, subject to cooling and cabling distance constraints, and (2) the subsystems may have different form factors. However, this type of packaging suffers from several operational disadvantages: (1) scaling difficulty; (2) cable management; (3) connector unreliability; and (4) unreliability of wire and cable assemblies. These problems contribute to the overall unreliability of today's high-performance computer and communications systems and lead to increased costs of ownership, maintenance, and upgrade of the systems.
The first disadvantage of current computer and communications systems is the difficulty one would encounter when the system's capacity or functions need to be expanded. This can occur even if a system was designed to accommodate a certain degree of growth. For example, to connect a new server into a network, additional communication cables need to be connected to a network switch. However, if the switch is fully allocated at capacity with insufficient free network ports, the upgrade becomes difficult and costly, particularly if the system must remain operational while the expansion is performed.
The second disadvantage of current computer and communications systems is the management of interconnect cabling and wiring. Given the large number of wires and cables in a computer facility, it is not uncommon that service and support personnel may incorrectly connect or disconnect a cable. The potential for other errors, such as plugging a cable into a wrong subsystem and leaving a cable unconnected, can also occur, particularly when system operation must be restored quickly. For optical cables, one must select the proper speed, wavelength, and distance parameters.
The third disadvantage of current computer and communications systems is the unreliability of connectors. Electrical connectors can degrade over time due to micro-fretting wear, which can lead to corrosion. As a metal connector corrodes, its electrical resistance increases, causing intermittent or hard failures in the system. Optical connectors may be mishandled, jarred, or contaminated by finger oil or dust, causing an intermittent open circuit in the system. In addition, optical-to-electrical transceivers can fail. These hazards and failures result in an increased cost of maintenance for the system.
The fourth disadvantage of current computer systems is the unreliability and cost of cables. Both electrical and optical cables can be broken, cracked, bent, compressed, or otherwise mishandled. Glass-based optical cables can also be damaged if stepped on or if the maximum bending radius is exceeded. Although cables are typically designed to meet certain system parameters, they are not always manufactured to such tolerances.
Electrical cables may also carry undesirable shield or ground currents between subsystems with chassis grounds or signal grounds at different electrical potentials, particularly when the subsystems are powered from different AC branch circuits. Cables can also undesirably pick up external electromagnetic interference or electrostatic discharges. These unwanted shield, ground, or signal currents can cause intermittent or hard errors in the communication between the subsystems, resulting in transient or hard failures in the whole systems.
The above disadvantages contribute to the unreliability, inflexibility, and high cost of ownership of existing computer and communications systems. Therefore, there remains a need for a modular computer system that has reliable and simple interconnection, and is easy to expand and service.